Aerosols, Chemistry and Climate

July 12th, 2008 by gavin

Everyone can probably agree that the climate system is complex. Not only do the vagaries of weather patterns and ocean currents make it hard to see climate changes, but the variability in what are often termed the Earth System components complicates the picture enormously. These components – specifically aerosols (particulates in the air – dust, soot, sulphates, nitrates, pollen etc.) and atmospheric chemistry (ozone, methane) – are both affected by climate and affect climate, since aerosols and ozone can interact, absorb, reflect or scatter solar and thermal radiation. This makes for a rich research environment, but can befuddle the unwary.

I occasionally marvel at the amount of nonsense that is written about climate change in the more excitable parts of the web, and most of the time, I don’t bother to comment. But in relation to the issue of aerosols, chemistry and climate, I read yesterday (h/t Atmoz) probably the most boneheaded article that I have seen in ages (and that’s saying a lot).

The hook for this piece of foolishness were two interesting articles published this week by Ruckstuhl and colleagues and a draft EPA report on the impacts of climate on air quality. First, Ruckstuhl et al found that as aerosols have decreased in Europe over the last few decades (as a result of environmental standards legislation), the amount of solar radiation at the ground has increased while the amount reflected to space has decreased. They hypothesize that this may have helped Europe warm faster in the last few decades than it would have otherwise done. Or equivalently, since the aerosols are anthropogenic, that European temperatures had been subdued due to the cooling effects of the aerosols – and since they are now decreasing, the full effects of the greenhouse gases are starting to be felt. This is just an update to the ‘global brightening‘ story we have touched on before. The EPA report is concerned with the impacts that climate change can have on atmospheric chemistry, and in particular the summertime peaks in urban ground-level ozone which are a well-known and serious health hazard. These are affected by local temperatures, cloudiness, temperature sensitive biogenic emissions and patterns of weather variability. Again, it is a story we have discussed before.

But the NewsBusters article succeeded in getting almost every aspect of these stories wrong. How do I correct thee? Let me count the ways.